1. Field of the Invention
The present invention relates to a positive resist composition suitably used in super micro lithography processes such as the manufacture of super LSI and high capacity microchips, and other photo-fabrication processes, and a pattern forming method using the same. More specifically, the invention relates to a positive resist composition capable of forming a highly precise pattern with KrF excimer laser rays, electron beams, EUV rays, etc., and a pattern forming method using the same.
2. Description of the Related Art
In the manufacturing process of semiconductor devices such as IC and LSI, fine processing by lithography with resist compositions has been conventionally performed. In recent years, with the increment of integration of integrated circuits, ultrafine pattern formation of the level of sub-micron and quarter-micron has come to be required. Under such a circumstance, the exposure wavelengths show a tendency to be shortening, such as from g-ray to i-ray, further to KrF excimer laser rays. Nowadays, further, the development of lithography using electron beams, X-rays or EUV rays, in addition to excimer laser rays, has been advanced.
As the resists suitable for far ultraviolet rays such as KrF excimer lasers, electron beams, X-rays, or EUV rays, “chemical amplification resists” using a radiation-sensitive acid generator capable of generating an acid upon irradiation (hereinafter also referred to as “exposure”) with actinic ray or radiation to increase sensitivity of the resists by means of the catalytic action of the generated acid are proposed. As the problem peculiar to such chemical amplification resists, the line width change of a resist pattern or T-shape formation due to the fluctuation of post exposure time delay (hereinafter also referred to as “PED”) from exposure to heating treatment after exposure has been conventionally pointed out. However, in late years, various kinds of chemical amplification resists applicable to the manufacture of devices have been proposed including a chemical amplification type radiation-sensitive resin composition using a polymer comprising a hydroxystyrene repeating unit, a t-butyl (meth)acrylate repeating unit, and a repeating unit lowering the solubility of the polymer in an alkali developer after exposure (JP-A-7-209868). However, with the trend of fining of devices of the present state, de-protective groups (a t-butyl protective group, etc.) ordinarily used in chemical amplification resists cannot reveal sufficient contrast, so that it is difficult for these resist compositions to be applied to the manufacture of devices of pattern size finer than now.
In this connection, some resist compositions are known, in which phenolic acid-decomposable resins obtained by copolymerization of acid-decomposable acrylate monomers having an alicyclic group as the de-protective group in place of a t-butyl protective group, etc., are used. For example, positive resist compositions disclosed in U.S. Pat. No. 5,561,194, JP-A-9-73173, JP-A-2001-166474, JP-A-2001-166478, JP-A-2003-107708 and JP-A-2001-194792 can be exemplified as these resist compositions. It is disclosed in JP-A-9-73173 that these resist compositions using acid-decomposable resins having such a de-protective group reveal high resolution.
On the other hand, line edge roughness increases in the degree of importance in late years with the progress of fining. Line edge roughness is minute irregularities of a nanometer scale formed on the sidewall of a pattern when fine lines are formed. Line edge roughness influences line width control, i.e., electrical characteristics of devices.
The above resist compositions using phenolic acid-decomposable resins obtained by copolymerization of acid-decomposable acrylate monomers having an alicyclic group as the de-protective group are not satisfactory with respect to line edge roughness. In addition, further improvement has been required in the point of line width change attendant upon variation of exposure amount, i.e., exposure latitude.